Virtual navigation (2255) and examination of virtual objects are enhanced using methods of insuring that an entire surface to be examined has been properly viewed. A user interface (FIG. 23) identifies regions which have not been subject to examination and provides a mechanism (2250) to route the user to these regions in the 3D display. Virtual examination is further improved by the use of measuring disks (905) to enhance quantitative measurements such as diameter, distance, volume and angle. Yet another enhancement to the virtual examination of objects is a method of electronic segmentation, or cleaning, which corrects for partial volume effects occurring in an object.